Magnetostrictive core production



- Jan. 3, 1961 D. E. PARKER ETAL MAGNETOSTRICTIVE CORE PRODUCTION Filed March 15, 1955 MAGNETOSTRICTIVE CORE PRODUCTION David E. Parker, Westerly, KL, and Keith E. Wetherbee,

Groton, Conn, assignors to the United States of America as represented by the Secretary of the Navy Filed Mar. 15, 1955, Ser. No. 494,588

12 Claims. (Cl. 29-1555) (Granted under Title 35, U.S. Code (1952), see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention concerns a method of producing magnetostrictive cores.

If ferromagnetic material, preferably of rod-shape, is placed in a magnetic field parallel to its major axis, the length of the material is changed. The length may increase or decrease, since the change in length is independent of the polarity of the applied magnetic field. The magnitude of the change in length of the material depends upon the material itself, the heat treatment and temperature of the material, and the degree of previous magnetization. The effect on mechanical dimensions of a magnetic field was discovered in 1847 by Joule and is called magnetostriction.

Important magnetostrictive materials, utilized in applications of magnetostrictive effect, are nickel and nickel alloys such as Permalloy, Nichrome and Monel metal. Nickel has the advantage, over its alloys, of being stable and reproducible even at commercial purities. The application of a magnetic field to nickel produces a stress in the nickel which causes it to contract in length. Under identical conditions Permalloy increases in length. The direction of internal stress in the material is independent of the direction of the applied magnetizing force.

Magnetostriction is reversible. If nickel is first magnetized and then stretched, the magnetization of the nickel decreases. If the nickel is compressed in length, its magnetization is increased.

Electroacoustical transducers may utilize the principle of magnetostriction in producing sound waves. In one such utilization, a nickel rod is subjected to an alternating magnetic field by an alternating current-eXcited-coil wound around the rod as a core. The rod length decreases periodically in response to the changing field. Since the variation in rod length is independent of the direction of the magnetic field, the rod elongates twice during each cycle of the alternating current. This may be prevented by the suitable premagnetization of the rod or by the transmission of a continuous direct current, known as a polarizing current, through the coil.

Magnetostrictive materials are susceptible to losses due to magnetic hysteresis. Since they are electrical conductors, magnetostrictive materials permit the flow of eddy currents whenever the magnetic flux through them changes. To keep these losses at a minimum the magnetostrictive core material may be employed in the form of laminations.

Prior art methods of producing laminated magnetostrictive cores comprise the following steps. Magnetostrictive material is prepared in the form of a metal strip and is mounted on a winding mandrel. The metal strip is spirally wound from the winding mandrel to a consolidating mandrel beneath the surface of evacuated liquid resin. When the winding process is completed the core is cured by being heated beneath the surface of resin for Y Patent Q several days.

When the resin is in a rubber-like solid state, the excess resin is removed from the core. The core is then further heated for about 12 hours, the consolidating mandrel is removed and the core is in operating condition.

The principal object of this invention is the provision of a method of producing laminated magnetostrictive cores substantially devoid of unfilled interlaminar gaps.

An object of this invention is the provision of a method of producing laminated magnetostrictive cores having interlaminar interspaces of less than one thousandth of an inch.

An object of this invention is the provision of a method of producing laminated magnetostrictive cores which may be performed entirely by machinery and which is amenable to mass production.

Another object of this invention is the provision of a method of producing laminated magnetostrictive cores of any desired size and of high quality.

A further object of this invention is the provision of a laminated magnetostrictive core of high quality and devoid of unfilled interlaminar gaps.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

Fig. l is an exaggerated presentation of the metal strip in the spiral form in which it is wound around a consolidating mandrel in the magnetostrictive core producing method of the present invention; and

Fig. 2 is a presentation of the spiral wound metal strip and mandrel in a resin bath which is part of the magnetostrictive core producing method of the present invention.

The method of the present invention for producing laminated magnetostrictive cores comprises the following steps.

Magnetostrictive material, such as nickel or alloys of nickel, is prepared in the form of a metal strip. The metal strip is tempered by heat treatment in accordance with the application planned for the completed transducer. Thus, if nickel is desired to be used in a polarized current, a nickel strip is heat-treated to temperatures, of about 900 degrees Centigrade, which produce full soft annealing characteristics. If nickel is desired to be used in a current that is not polarized, a nickel strip is heattreated to temperatures, of about 600 degrees centigrade, which produce half-hard nickel.

After heat-treatment the metal strip is coated with an electrical insulating material which adheres to the metal and which may be applied smoothly in thicknesses of about one ten thousandth of an inch. The electrical insulating material may be selected from those well known in the art which are suitable for the purposes of the present invention. The selected electrical insulating material should be adhesive. One such material is Alundum.

After the application of the insulating material to the metal strip, a spacing strip, or interlay, composed of cotton or linen is joined to the insulated surface of the metal strip by adhesion. The spacing strip may be suitably dimensioned at a thickness of five thousandths of an inch and at a width of five-tenths of an inch.

The metal strip and the spacing strip adhering to it are wound around a consolidating mandrel in fiat spiral fashion.

Any suitable means, besides a mandrel, may be employed to maintain the metal strip in fiat spiral form. Thus, the metal strip may be initially clamped in spiral position, thereby eliminating the necessity for a mandrel.

The metal strip 1 is shown loosely wound in spiral fashion for the purpose of clarity in presentation. The

3 metal strip 1 has a pair of dotted lines running along its outer surface. This outer surface is coated with electrical insulating material upon which is adhered the spacing strip represented by the pair of dotted lines.

After the metal strip is wound around the consolidating mandrel, the wound metal strip and mandrel are completely submerged in a resin bath. The bath is heated to about 160 degrees Farenheit and evacuated, by means well known in the art. Evacuation is maintained for about one hour. The resin may be selected from those well known in the art which are suitable for the purposes of the present invention. One such resin is a phenolic condensation product.

The resin bath 2 is maintained in the container 3 which supports the consolidating mandrel 4. The metal strip 1 is wound around the mandrel 4 in flat spiral fashion. Any of many means well known in the art may be employed to heat the bath as desired and to evacuate the bath as desired. The bath is heated and then evacuated in order to aid resin penetration of the interlaminar areas, or the spaces between the metal strip surfaces. Volatile products inherent in resin are eliminated by the evacuation.

After an evacuation of about one hour the spacing strip is removed from the spaces between the surfaces of the spiral wound metal strip.

After removal of the spacing strip the resin bath is reheated to 160 degrees Farenheit and re-evacuated. The spiral wound metal strip is tightened around the mandrel and clamped in position.

If the metal strip is initially clamped into spiral form without the aid of a mandrel, then, after re-evacuation, it is tightened and then reclamped in (a tighter flat spiral) position.

The clamped spiral wound metal strip is essentially the magnetostrictive core produced by the method of the present invention but is further treated before becoming a finished product. It is cured by being heated in a resin bath, to a temperature of about 160 degrees Farenheit, to prevent oozing of the resin from the interlaminar areas. The bath temperature is maintained at 160 degrees Farenheit.

When the resin is in a rubber-like solid state, which may be after several days in the bath, excess resin which isthat serving no useful purpose is removed from the core. After the removal of excess resin, the core is further heated to, and maintained at, about 200 degrees Farenheit for about 12 hours.

After the further heat treatment the mandrel is removed from the center of the core. The finished core 1s then ready for use.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

We claim:

1. The method of producing a magnetostrictive core which comprises heat treating a strip of magnetostrictive metal for its intended ultimate use, coating the heat treated strip with an adherent electrical insulating material, winding the coated strip into a scroll around a form with a temporary ribbon-like interlay tape acting as a spacer between adjacent turns of the scroll, submerging the Scroll and form in a resin bath in a closed chamber, heating the submerged scroll and resin, to about 160 F. while lowering the atmospheric pressure in said chamber for a period of time adequate to facilitate substantial penetration of the resin into the spaces between adjacent turns of the scroll and remove any volatile products inherent in the resin, then physically removing the interlay as a unit from between the layers of the scroll, continuing heating of the scroll and resin so freed of the interlay to about 160 F. under lowered atmospheric pressure to facilitate further penetration of the resin with 4 the space between adjacent turns previously occupied by said interlay, next tightening the scroll around the form and securing it in that condition, then curing, at about F., the scroll, while it is beneath the surface of the resin to prevent the resin from oozing out of the interstices, until the resin becomes a rubber-like solid, then removing from the scroll excess resin that serves no useful purpose, then continuing the curing of the scroll with adhering resin at about 200 F. for about 12 hours, and then removing the form from the scroll.

2. The method as set forth in claim 1, wherein said heating of the submerged scroll and form is continued for about one hour.

3. The method as set forth in claim 1, wherein said interlay is materially narrower than said strip.

4. The method as set forth in claim 1, wherein said winding of the coated strip and interlay into a scroll around a form is performed in air.

5. The method as set forth in claim 1, wherein said winding of the coated strip and interlay into a scroll around a form is performed in air and said heating of the submerged scroll and form is continued for about one hour.

6. The method of producing a magnetostrictive core which comprises winding a strip of magnetostrictive metal coated with electrical insulating material into a scroll form with a temporary spacer ribbon-like tape of lesser width than the strip interposed between successive turns of the strip, submerging the scroll in a resin bath in a closed chamber, heating the submerged scroll and resin while lowering the atmospheric pressure in the chamber to facilitate penetration of the bath between adjacent turns of the strip, then removing the temporary spacer tape as a physical body from between the successive layers of the strip, continuing heating of the scroll and resin so freed of the spacer tape, with lowered atmospheric pressure in said chamber to facilitate penetration of the resin into the space between adjacent turns of the strip previously occupied by said tape, until the resin becomes rubberlike, removing excess rubber-like resin from the scroll, and then curing the scroll with adhering resin.

7- The method as set forth in claim 6, wherein the curing is at a temperature of about 200 F. for about 12 hours.

8- The method as set forth in claim 6, wherein the winding of the metal strip into a scroll is upon a form on which the strip remains until after the curing.

9. The method as set forth in claim 6, wherein the heating in said closed chamber is at a temperature of about 160 F. and the curing is at a temperature of about 200 F. for about 12 hours.

10. The method of producing a magnetostrictive core which comprises heat treating a strip of magnetostrictive metal for its intended ultimate use, coating the heat treated strip with an adherent electrical insulating material, winding the coated strip into a scroll around a form with a temporary ribbon-like interlay tape continuing from end to end of the scroll and acting as a spacer between adjacent turns of the scroll, submerging the scroll and form with interposed tape in a resin bath in a closed chamber, heating the submerged scroll and resin bath, while lowering the atmospheric pressure in Said chamber to faciltate penetration of the resin into the spaces between adjacent turns of the scroll and remove any volatile products inherent in the resin, then physically removing the interlay as a unit from between the layers of the scroll, continuing heating of the scroll and resin bath so freed of the interlay under lowered atmospheric pressure to facilitate penetration of the resin into the space between adjacent turns of the strip previously occupied by said interlay, next tightening the scroll around the form and securing it in that condition, then curing the resin on the scroll, while the scroll is beneath the surface of the resin to prevent the resin from oozing out from between adjacent turns of the scroll until the resin becomes a rubber-like solid, then removing excess resin from the scroll, then continuing the curing of the scroll with adhering resin, and then removing the form from the scroll.

11. The method of producing a magnetostrictive core which comprises heat treating a ribbon-like, flexible strip of magnetostrictive metal for its intended ultimate use, then applying to one face of said treated strip a very thin coating of an adherent, electrically insulating material, releasably confining face to face to such coated face of the metal strip, a thin flexible non-metallic spacing strip of less width than said metal strip and approximately continuous from end to end of the said metal strip, then winding the two strips together into a flat spiral form about a suitable mandrel, then submerging the mandrel and strips wound thereon in a heated bath of polymerizable resin, evacuating the bath while the mandrel and strips are submerged therein to facilitate penetration of the resin between the adjacent turns of the metal strips and eliminate volatile components from the resin, then physically removing the spacing strip from between the turns of the other strip, then tightening the metal strip upon the mandrel and securing it in tightened condition, then curing the resin of the bath with tightened metal strip therein until the resin has a consistency approximating that of rubber, then removing excess resin from the spiral strip, then continuing the polymerization of the resin on the spiral strip, and then removing the mandrel from the strip.

12. The method of producing a magnetostrictive core which comprises applying to one face of a ribbon-like, flexible strip of magnetostrictive metal a very thin coating of an adherent, electrically insulating material, re-

leasably confining face to face to such coated face of the metal strip for substantially the full length of such strip, a thin, continuous, flexible non-metallic spacing strip of less width than said metal strip, then winding the two strips together into a flat spiral form about a suitable mandrel, then submerging the mandrel and strips wound thereon in a heated bath of polymerizable resin, evacuating the bath while the mandrel and strips are submerged therein to facilitate penetration of the resin between the adjacent turns of the metal strip and eliminate volatile components from the resin, then physically removing the spacing strip from between the turns of the other strip, then curing the resin of the bath with metal strip therein until the resin has a consistency approximating that of rubber, then removing excess resin from the spiral strip, then continuing the polymerization of the resin on the spiral strip, and then removing the mandrel from the strip.

References Cited in the file of this patent UNITED STATES PATENTS 2,261,983 Ford Nov. 11, 1941 2,391,229 DEntremont Dec. 18, 1945 2,484,214 Ford et al. Oct. 11, 1949 2,579,560 Ford Dec. 25, 1951 2,623,920 Ford Dec. 30, 1952 2,700,207 Zimsky Jan. 25, 1955 2,702,935 Kyle Mar. 1, 1955 FOREIGN PATENTS 611,953 Great Britain Nov. 5, 1948 696,346 Great Britain Aug. 26, 1953 

1. THE METHOD OF PRODUCING A MAGNETOSTRICTIVE CORE WHICH COMPRISES HEAT TREATING A STRIP OF MAGNETOSTRICTIVE METAL FOR ITS INTENDED ULTIMATE USE, COATING THE HEAT TREATED STRIP WITH AN ADHERENT ELECTRICAL INSULATING MATERIAL, WINDING THE COATED STRIP INTO A SCROLL AROUND A FORM WITH A TEMPORARY RIBBON-LIKE INTERLAY TAPE ACTING AS A SPACER BETWEEN ADJACENT TURNS OF THE SCROLL, SUBMERGING THE SCROLL AND FORM IN A RESIN BATH IN A CLOSED CHAMBER, HEATING THE SUBMERGED SCROLL AND RESIN, TO ABOUT 160* F. WHILE LOWERING THE ATMOSPHERIC PRESSURE IN SAID CHAMBER FOR A PERIOD OF TIME ADEQUATE TO FACILITATE SUBSTANTIAL PENETRATION OF THE RESIN INTO THE SPACES BETWEEN ADJACENT TURNS OF THE SCROLL AND REMOVE ANY VOLATILE PRODUCTS INHERENT IN THE RESIN, THEN PHYSICALLY REMOVING THE INTERLAY AS A UNIT FROM BETWEEN THE LAYERS OF THE SCROLL, CONTINUING HEATING OF THE SCROLL AND RESIN SO FREED OF THE INTERLAY TO ABOUT 160*F. UNDER LOWERED ATMOSPHERIC PRESSURE TO FACILITATE FURTHER PENETRATION OF THE RESIN WITH THE SPACE BETWEEN ADJACENT TURNS PREVIOUSLY OCCUPIED BY SAID INTERLAY, NEXT TIGHTENING THE SCROLL AROUND THE FORM AND SECURING IT IN THAT CONDITION, THEN CURING, AT ABOUT 160*F., THE SCROLL, WHILE IT IS BENEATH THE SURFACE OF THE RESIN TO PREVENT THE RESIN FROM OOZING OUT OF THE INTERSTICES, UNTIL THE RESIN BECOMES A RUBBER-LIKE SOLID, THEN REMOVING FROM THE SCROLL EXCESS RESIN THAT SERVES NO USEFUL PURPOSE, THEN CONTINUING THE CURING OF THE SCROLL WITH ADHERING RESIN AT ABOUT 200*F. FOR ABOUT 12 HOURS, AND THEN REMOVING THE FORM FROM THE SCROLL. 